Compound A (4,5,6,7-Tetrahydro-11-methoxy-2-[(4-methyl-1-piperazinyl)methyl]-1H-cyclopenta[a]pyrrolo[3,4-c]carbazole-1,3(2H)-dione) is a PARP (poly ADP-ribose polymerase) inhibitor for use in the treatment of breast, ovarian, and other cancers, either alone or in conjunction with chemotherapy or radiotherapy. See, e.g., U.S. Pat. Nos. 7,122,679; 8,716,493; and 8,633,314.

Compound A is a prodrug of Compound B:

The free base form of Compound A forms hydrates, which are undesirable. In addition, the free base form of Compound A has a low bulk density, impeding manufacturing. Alternative forms of Compound A are needed.